1. Field
This disclosure generally relates to readers configured to read machine-readable symbols.
2. Description of the Related Art
Machine-readable symbols are generally formed using one or more machine-readable symbol characters selected from a machine-readable symbology. One-dimensional (“1D”) or linear machine-readable symbols contain information generally encoded in the spacing between leading and trailing edges of successive marks, typically formed as a series of lines and/or spaces and often colloquially referred to as “barcode symbols.” Two-dimensional (“2D”) machine-readable symbols contain information generally encoded in the spacing or position of polygonal patches. Two-dimensional machine readable symbols may be formed from characters selected from area code or matrix code symbologies. Two-dimensional machine readable symbols typically encode information in a higher density format than one dimensional machine readable symbols. Machine-readable symbols can be generated using virtually any media (e.g., ink, toner, etching, and the like on a solid substrate or an image formed using monochromatic or multicolor pixels on a display device, to provide just a few examples) and can be placed upon any media (e.g., paper, plastic, metal, cloth, and/or an electronic display, to provide just a few examples).
The use of machine-readable symbols to optically encode information extends back 60 years to the first U.S. patent granted in 1952 for a “bull's-eye” type machine-readable symbol intended for use in the retail grocery business (U.S. Pat. No. 2,612,994 to Woodland, et al., entitled “Classifying Apparatus and Method”). In the intervening 60 years many additional types of machine-readable symbologies have been proposed with several, such as the one dimensional Universal Product Code (“UPCs”), gaining widespread acceptance. The early data limitations of one-dimensional machine-readable symbols (e.g., barcode symbols) have been at least partially remedied through the more recent adoption of two-dimensional machine-readable symbols.
The use of machine-readable symbols has expanded well beyond the original product identification role envisioned in 1952. Today, one and two dimensional machine-readable symbols (generically “machine-readable symbols”) can be found on railcars, automotive parts, driver's licenses, advertisements, shipping labels, and even on packaging. With the increasing prevalence of machine-readable symbols in everyday life, the type of media used to form the machine-readable symbol and the substrate upon which the machine-readable symbol is displayed also continue to increase. Machine-readable symbols can be visibly printed or otherwise formed using conventional inks and/or printing technologies such that the resulting machine-readable symbol is visible to humans without aid. Alternatively, machine-readable symbols can be invisibly printed using specialized inks such as infrared or ultraviolet fluorescing materials rendering the resultant machine-readable symbols invisible to an unaided human observer. While typically formed as a binary image (e.g., black and white) some symbologies display color, for example to increase data or information density of the resulting machine-readable symbols. Machine-readable symbols can also form part of a security feature, for example where the machine-readable symbols are printed in multiple colors or printed using a partially or completely invisible medium, for example an ink reflective only in the infrared electromagnetic spectrum.
Post offices around the world have adopted various machine-readable symbologies which has resulted in machine-readable symbols in a wide variety of shapes, forms, and styles. Such symbols may provide concisely printed postage, class of service, and other relevant shipping (e.g., origination and/or destination addresses), tracking and payment data directly on a face of letters, parcels, and other packages. The increasing use of diverse forms of symbologies on items in commerce has generated a need for machine-readable symbol readers capable of quickly and easily adapting to a multitude of machine-readable symbol styles and symbologies.